Polyethylene glycol ester is a mono or diester of a fatty acid or oil reacted with a polyethylene glycol. It has been widely used as emulsifiers, pearlizers, stabilizers, solublizers or viscosity-controlling agent especially in household and cosmetic products such as lotion, cream, hand soap, shampoo and so on. Owing to its versatility in different filed of application, numerous effort has been contributed to improve the existing polyethylene glycol ester types or devise a new types of polyethylene glycol ester derivatives with improved properties. Furthermore, improvement also been made to enhance the rate, selectivity, or efficiency of the esterification reaction.
Patent Publication no WO2007038025 filed an application on an improved process which able to produce high purity of polyol monoester. This application claims that pre-heating of the polyols before reacting with the fatty acid or its derivatives can attain the purpose of producing high fraction of polyol monoester. In the disclosed examples, sodium methoxide is employed as the catalysts to enhance the reaction.
Lee et.al. have filed a U.S. Pat. No. 6,723,863 regarding a method for tranesterification of polyols and fatty acids in the absence of oxygen. Such approach claims to be effective in avoiding unnecessary oxidation of the reaction product.
Another United State patent with publication no. 2005159610 discloses a process to produce polyol esters which is light in colour by end of the process without requiring further distillation or de-colouring. Particularly, the fatty acid C1 to C5 alkyl esters are reacted with polyols in the presence of catalysts and borohydride in which sodium methoxide is employed as the catalysts.
U.S. Pat. No. 3,669,848 relates to a method to produce propylene glycol monoester with low fraction of diester product by conducting the reaction in vacuum distillation between the temperature of 170° C. to 285° C. under negative pressure.
European patent with publication no. 1681281 claims a method of producing fatty acid monoesters by means of esterification between alcohol and a compound that is selected from a fat of animal origin, a fat of vegetable origin, and a fatty acid methyl ester. This invention employs basic solid catalysts which are monovalent or polyvalent metal oxides as the catalysts to enhance the reaction. With the aid of solid catalysts, the problems like presence of catalysts residues in the end products can be prevented.
U.S. Pat. No. 5,675,032 discloses a process for preparation of polyethylene glycol di (2-(4-chloro-2-methylphenoxy)-propionic acid ester mixtures by reaction between 2-(4-chloro-2-methylphenoxy)-propionic acid and a mixture of different types of polyethylene glycol. Along the reaction of this invention no catalyst employed.
Most of the processes now available for the production of polyethylene glycol ester or its derivatives are mainly employed strong acids or bases as the catalysts which may render the process uncontrollable due to the drastic condition applied. Over oxidation is common in such condition that lead to production of different unwanted side products thus affect the quality of the end products derives thereof. Moreover, tedious processes are required to get rid of the catalysts residues in the produced polyethylene glycol by end of the esterification because presence of catalysts residue in the polyethylene glycol ester produced is detrimental to the end product derives thereof. In the esterification processes, it is found impractical to reuse the catalysts too as the homogenous catalysts used is impossible to be extracted intact from a pool of polyethylene glycol ester produced while heterogenous catalysts are normally degraded due to the drastic condition after the process. Therefore, it is ideal to the esterification process progress smoothly without the need of drastic condition to enhance the rate of the reaction, specifically a self-initiated reaction under suitable condition without the use of catalysts.